Multiple wireless communication protocols may often simultaneously operate within the same radiofrequency band. For example, a variety of wireless communication protocols operate in the industrial, scientific, and medical (ISM) band defined by the ITU-R in 5.138, 5.150, and 5.280 of the radio regulations. These wireless communication protocols operating in the ISM band include band converted variations of the digital enhanced cordless telecommunications (DECT) protocol, IEEE 802.11 (also referred to herein simply as “802.11”), and Bluetooth. Where multiple frequency-overlapping wireless communication protocols are simultaneously in operation in a given region, interference across networks can undesirably affect performance of one or more systems.
For example, a DECT system monitors channels using a least-interfered-channel/listen-before-talk algorithm to select a channel and timeslot to use, and a move-on-error algorithm to change channels when corruption is observed on a link already set up. Unfortunately, for the case of sharing spectrum between a DECT-protocol-derivative product and an 802.11-protocol service, DECT's least-interfered channel algorithm does not detect 802.11-protocol usage of 802.11 channels efficiently. The DECT scanning algorithm was designed for a dedicated band. The major problems with using such an approach in a band shared with other protocols are due to the fact that 802.11 traffic is bursty. A channel may be in use by the 802.11 protocol for short bursts only, and very irregularly. As a result, the typical DECT-standard monitoring process of periodically measuring the signal level in a channel and timeslot, while effective at determining the channel/timeslot occupancy by another DECT system, does not typically detect the presence of an 802.11 system using that channel.
FIG. 1A illustrates the detection method which DECT-derived products use to validate that a channel is free to use prior to starting transmissions on that channel. The DECT-derived system checks the candidate channel list periodically, looking at the signal level during one DECT timeslot, from time to time, to see if that timeslot is unused on that channel. The prior art DECT scanning system utilizes a round-robin scanning algorithm. The scanning algorithm tests twenty-four timeslots in one DECT TDMA frame on channel N, N+1, N+2 . . . N+M−3, N+M−2, N+M−1. The scan for other user activity repeats for M total channels. If the interference source is continuous, or if it repeats at 10 ms intervals, the testing will catch the usage of the channel by the other user. 802.11 usage, though, may be at other rates; commonly the 802.11 access points transmit a beacon every 100 ms, but data may be present or not at any time on the channel. The test of channel N may miss IEEE 802.11 activity on channel N in the round-robin period scanning algorithm.
In one prior art solution, more long-term observation time is dedicated to each channel and timeslot so as to increase the probability of observing a short burst. This approach is problematic in that there are up to 86 channels and 12 duplex timeslot pairs. If other-user bursts occur at the rate of one per second for a lightly loaded channel, the probability of detection remains low for any individual monitoring event if there are many timeslots and channels to scan, and usage of any channel/timeslot combination by an other-user service is irregular, so many monitoring events are required. With the high number of channels and timeslots to observe, reliable qualification and ranking of available native DECT protocol channels for the 802.11 interferer protocol interference is slow, resulting in undesirably-slow state-changes on entering service, coming into range, or in responding to changes in an agile 802.11 system.
In one prior art solution, an IT manager using a central management tool configures the DECT system by assigning certain channels for use. The IEEE 802.11 system is separately configured to use channels from its own selectable channel list which would not overlap with the selected DECT channels in use. While this approach addresses some of the technical issues, it requires action by the IT manager and does not result in an individual DECT unit being optimally configured for the environment in its physical proximity. The resulting implementation imposes inefficiencies on both the DECT system installation and on the 802.11 installation. On the 802.11 side, such manual planning prevents the 802.11 system from being frequency-agile in response to changes in load. With respect to the DECT system, locking out all 802.11-used-channels in a multi-DECT-unit deployment area precludes the use of channels that happen to be not in use by the 802.11 system in a particular DECT unit's locale, which reduces the possible density for the DECT system.
Thus, improved systems and methods for services in a shared frequency band provided by different protocols are needed.